I. Field of the invention
The present invention relates to a driver circuit for simultaneously and rapidly setting a plurality of output buffers of a three-state gate array into and out of a floating third state with the employment of a low driving current.
II. Description of the Prior Art
Gate array circuits are well-known in the prior art. Such circuits typically include the standard configuration of components such as input/output pins, gates, output buffers, and drivers each having terminals which can be interconnected through one or more metallization layers. The user of such a gate array selects a particular standardized configuration of components and then designs a few unique metallization layer patterns to connect the standard configuration of components into a customized configuration. Such metallization layers are typically high density and, therefore, require as thin a width for each conductor in the metallization layer as possible.
As described in more detail below, prior art gate array circuits typically suffer from the requirement of a large current control signal for setting each member of a particular group of output buffers into a third or floating state. Since many output buffers are controlled simultaneously by the same third state control signal, preferably one control line would be used in a fan-out fashion to provide the third state control signal to a plurality of output buffers. However, in view of the large current requirements, standard width conductors cannot carry the current which would be required in such a fan-out arrangement. Accordingly, individual control lines are required for each third state control input of an output buffer, thereby negatively contributing to the density problem inherent in prior art gate arrays.
It is an object of the present invention to provide a driver circuit for a gate array which permits control of a floating state in a plurality of output buffers using a single, narrow width fanned-out conductor for each group of output buffers.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned from practice of the invention.